Sheet stretching structure and sheet grippers for use therein



March 9, 1965 J. A. GLOSSMANN 3,172,151

SHEET STRETCHING STRUCTURE AND SHEETGRIPPERS FOR USE THEREIN 5 Sheets-Sheet 1 Filed March 21, 1963 Fig. 1

Jn venfor Johannes Albin G'lassmann March 9, 1965 J. A. GLOSSMANN 3,172,151

SHEET STRETCHING STRUCTURE AND SHEET GRIPPERS FOR USE THEREIN Filed March 21, 1963 S Sheets-Sheet 2 .70 ven for: filzanne 5' 741,5"? Qfossman n Jfiichael ST sari/32 his Auw'ney March 1965 J. A. GLOSSMANN 3,172,151

SHEET STRETCHING STRUCTURE AND SHEET GRIPPERS FOR USE THEREIN Filed March 21. 1963 3 Sheets-Sheet 3 Fig. 4

Fig. 5

Jnven/ar: 1014021111 es fllbin Glassmd n 1111mm 9. en-Ker [11's vqtiorne United States Patent 3,172,151 SEEET STRETCHING STRUCTURE AND SHEET GRIPPERS FOR USE THEREDJ Johannes Albin Glossmann, Baden-Wurttemberg, Germany, assignor to Henschel-Werke Airtiengesellschaft, Kassel, Germany Filed Mar. 21, 1963, Ser. No. 267,021 Claims priority, application Gerrnany, Mar. 24, 1962,

58 12 Claims. (Cl. 18--1) The present invention relates to sheet stretching apparatus and in particular to a sheet gripping device which is adapted to be used in such an apparatus.

As is well known, it is required in the treatment of certain sheets to stretch the sheets both longitudinally and transversely. Thus, depending upon whether the sheet has been calendered, cast, or extruded, the sheet will be stretched longitudinally and transversely in order to provide, through proper orientation of the molecules of the sheet, a greater strength of the sheet, greater uniformity in its properties, or greater transparency inasmuch as some sheets can be rendered more transparent by such stretching thereof. In the event that the longitudinal and transverse stretching of such a sheet takes place one subsequently to the other, it is required that the arrangement of the molecules be changed twice, which very often results in damaging of the sheet or in any event in very diflicul-t handling thereof during the second change in the orientation of the molecules. Even though there are known devices for stretching a sheet simultaneously both longitudinally and transversely, these known devices make it very difficult to control the extent of transverse stretching in synchro-nism with the extent of longitudinal stretching, and in most known machines the structure for transversely stretching the sheet opposes the operation of the structure for longitudinally advancing the sheet, which is also extremely undesirable. Moreover, with known structures the gripping devices which engage the sheet unavoidably damage the sheet undesirably either by forming holes which pass through the sheet or by unavoidably deforming the sheet.

It is accordingly a primary object of the present invention to provide an apparatus which will avoid the above drawbacks.

Thus, one of the objects of the present invention is to provide a sheet-gripping device which will reliably grip a sheet during longitudinal and transverse stretching thereof while at the same time avoiding the possibility of any damage to the sheet at the places where it is gripped.

Another object of the present invention is to provide a sheet-gripping structure which is capable of effecting both the longitudinal and transverse stretching of the sheet in such a way that the interrelationship between the longitudinal and transverse stretching can be precisely controlled.

It is furthermore an object of the present invention to provide a sheet-gripping device which forms part of a sheet-stretching apparatus and which is capable of being reliably guided through the apparatus as well as of being conveniently handled to attach a sheet to and to remove the sheet from the gripping device.

It is furtherm-ore an object of the present invention to provide a sheet-stretching apparatus which is capable of longitudinally and transversely stretching the sheet in such a way that the extent and rate of transverse stretching of the sheet can be precisely synchronized with the extent and rate of longitudinal stretching of the sheet so as to provide the desired orientation of the molecules of the sheet.

Also, the object of the present invention includes the provision of a sheet-gripping device which is characterized 3,172,151 Patented Mar. 9, 1965 by great strength as well as simplicity in construction and reliability in operation.

With the above objects in view the invention includes, in a sheet stretching apparatus, a drawing means which draws a sheet longitudinally through a predetermined drawing field while simultaneously longitudinally stretching the sheet as it passes through the drawing field. A pair of gripping means respectively grip the sheet at opposed side edge portions thereof, and a guide means is located along opposite sides of the drawing field and guides the pair of gripping means for movement along the drawing field together with the sheet, this guide means increasing the distance between the pair of gripping means as the latter advance with the sheet along the drawing field so that the sheet is stretched transversely simul taneously with the longitudinal stretching thereof.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 diagrammatically illustrates in a top plan View one possible apparatus according to the invention tor longitudinally and transversely stretching a sheet;

FIG. 2 is a top plan view of a gripping device according to the invention, FIG. 2 showing in dot-dash lines a guide means which guides the gripping means of FIG. 2;

FIG. 3 is a front elevation of the structure shown in FIG. 2;

FIG. 4 is a view of the structure of FIG. 2 as seen from the lefit side of FIG. 2; and

FIG. 5 is a view of the structure of FIG. 2 as seen from the right side of FIG. 2.

Referring to FIG. 1, there is illustrated therein a sheet 2 which is stretched both longitudinally and transversely, as indicated by the arrows 5 and 6 in FIG. 1. A drawing means is provided for advancing the sheet 2 through ice a substantially horizontal drawing field in which the sheet 2 is located in FIG. 1, and this drawing means will stretch' the sheet longitudinally in the direction of the arrow 5 simultaneously with movement of the sheet through the drawing field. The drawing means includes a pair of drawing rollers 3 located at the entrance end of the drawing field and a pair of drawing rollers 4 located at the discharge end of the drawing field, and the drive which rotates the drawing rollers 4 turns these rollers at a speed greater than the rollers 3 so that the sheet is necessarily stretched longitudinally while advancing through the drawing field. The drive for the rollers 4 is controlled in a well known manner so that the extent and rate of longitudinal stretching of the sheet as it passes through the drawing field can be regulated. Depending upon the nature of the plastic sheet material 2, heat will be applied to the sheet in accordance with the characteristics thereof and the heated sheet will be longitudinally stretched while passing through the drawing field also at a rate and extent determined by the nature of the material of the sheet.

In accordance with the present invention the sheet 2 is gripped at edge portions thereof by a plurality of gripping devices which are entirely unconnected from each other and which travel with the sheet 2 as the latter advances along the drawing field. The gripping devices 1 of the invention are shown in FIG. 1 adjacent the discharge end of the drawing field. A guide means 7, 7' is provided for guiding the pair of gripping means 1 while the latter grip opposed side edge portions of the sheet 2, and the guide means 7, 7 guides the pair of gripping means 1 for movement with the sheet 2 along the draw ing field while at the same time the guide means 7, 7' increases the distance between the pair of gripping means 1 as the latter advance with the sheet in the direction of the arrow so that in this way the sheet is stretched transversely, as indicated by the arrow 6, simultaneously with the longitudinal stretching thereof. It will be noted that the inner sides of the pair of endless guides 7 and 7' extend along the drawing field while located at opposite sides thereof, and at the entrance end of the drawing field the inner portions of the guides 7 and 7 are located relatively close to each other and extend parallel to each other while these inner portions of the guides then extend along curved paths while diverging from each other so that it is possible with this construction to stretch the sheet transversely in dependence upon the extent of longitudinal stretching thereof, and also the transverse and longitudinal stretching take place simultaneously.

As is apparent from FIG. 1, the drawing rollers 3 and 4 are carried by a table the top surface of which forms a support means for the structure of the invention, and the endless rods 7 and 7' are suitably carried by this table. Each of the endless rods 7 and 7', which form the guide means of the invention, is composed of successive rod sections which are pivotally hinged to each other, and the ivot pins are in turn supported by blocks located beneath the rods 7 and 7' and supported in suitable guide slots of the table so that these blocks can be shifted laterally and in this way determine the distance between the inner runs of the guide rods 7 and 7' so as to determine the distance between the pair of gripping means 1 as the latter advance with the sheet through the drawingfield. The structure for adjusting the blocks and holding them in their adjusted positions so as to determine the configuration of the guide means 7 and 7' forms no part of the present invention and is therefore not illustrated. With this construction it is possible to precisely set the manner in which the the pair of gripping means 1 are displaced apart from each other as they advance longitudinally along the drawing field and by changing the speed of revolution of the discharge rollers 4 of the drawing means it is possible to provide a synchronized control in the rate and extent of longitudinal and transverse stretching of the sheet so that the manner in which the sheet is treated can be very precisely controlled with the structure of the invention. The adjustment of the guide rods 7 and 7', which have a circular cross section, and the regulation of the speed of the discharge rollers 4 of the drawing means can be derived from a central control station.

The gripping devices 1 of the invention serve the purpose of holding and guiding the sheet so as to support the latter during the longitudinal stretching thereof and in addition the gripping devices of the invention act directly upon the sheet to effect the transverse stretching thereof.

Referring now to FIGS. 2-5, it will be seen that each gripping device of the invention includes a main body 8 made of any suitable rigid material such as a suitable metal. The main body- 8 has an outer end which is located distant from the drawing field, and at its outer end the main body 8 turnably carries a guide roller 9 which forms one of a plurality of rollers of an assembly of rollers carried by the main body 8 of each gripping means 1. It is the guide rollers 9 which principally absorb the transverse forces set up during the transverse stretching of the sheet, these transverse forces being absorbed by the rollers 9 as the latter roll along the guide means formed by the rods 7 and 7'. The roller assembly of each gripping means includes also a supporting roller 10 which also rolls along the guide rod 7, and the axis of the supporting roller 10 is inclined to the substantially vertical axis of the guide roller 9, and in addition the guide roller 10 is located at an elevation higher than the guide roller 9. As is apparent particularly from FIGS. 4 and 5, the guide roller 9 engages the outer surface portion of the guide rod 7 at the portion thereof which extends along the drawing field while the supporting roller 10 engages an inner upper portion of the surface of the guide rod 7, this inner upper portion being located directly next to thedrawing field. As is apparent from FIGS. 4 and 5, the rod 7 is of circular cross section and the rollers 9 and 10 have concave peripheries which mate with the convex surface of the guide rods 7, and in addition these rollers 9 and 10 extend beyond the center of the guide rod 7 so that in this way the rollers 9 and 10 cooperate to hold the gripping device on the rod 7, preventing separation of each gripping means from the rod 7, and in addition the diameters of the rollers 9 and 10 are such that they are capable of executing the necessary changes in direction provided by the curved guide rods 7 and 7 during. the stretching of the sheet. The roller 9 is supported for rotary movement by a shaft 9' carried by the main body 8, while the roller 10 extends through an opening in the main body 8 and is supported for rotary movement by' the inclined shaft 16), and the axis of the shaft 19, which forms the axis of turning of the roller 10, intersects the am's of the shaft W, which forms the axis of turning of' the roller S at an acute angle at an elevation higher than the horizontal drawing field, the axis of the shaft 10 be-- coming located at greater distances from the axis of the shaft a as the axis of the shaft 10' passes downwardly to the drawing field from the intersection between the axes. of the shafts 9 and 16), respectively.

At the front end of the main body 8, which is the left end thereof as viewed in FIGS. 2 and 3, this main body 8 carries a guide roller 11 which is turntable about a: vertical axis and which engages the inner side surfaceof each guide rod 7 and 7', and the purpose of this leading roller 11 is to enable the operator to locate the grip-- ping means at a selected position on the guide means 7, '7' as well as to position successive gripping means. at selected distances from each other.

At its inner lower portion the main body 8 carries apair of supporting rollers 12 which are supported for: rotation by a pair of horizontal shafts 12', respectively, and these rollers 12 engage the surface of the table shown in FIG. 1 adjacent the entrance and discharge ends of gripping means from the sheet 2'. Moreover the rollers 12 cooperate with the supporting surface to support the guide body 8 of the gripping means during return of the. gripping means to the starting position thereof.

The main body 8 is also formed with acutout 13 at its underside which is adapted to receive a projection of a drive means which serves to return the gripping; Moreover, there is located at the under side of the main body 8 a guide roller' means to the starting position.

17 supported by a shaft 17' for rotation about a vertical axls and also coacting with a. structure which returns the gripping means to its starting position.

The main body 8 of each gripping means 1 turnably' supports a front gripping lever 14 which guarantees that the gripping means will advance with the sheetlongitudinally along the drawing field even if there is no particular lateral or transverse stretching of the sheet and which also prevents the sheet from being withdrawn from the gripping levers 15 and 16, which act to hold the sheet transversely, as a result of the longitudinal stretching of the sheet. As is apparent particularly from FIG. 3, the lever 14 is turnable about an axis which extends across the drawing field and is located over the drawing field in a counterclockwise direction, as viewed in FIG. 3, to an inoperative position where the lower curved end of the lever 14. is spaced from the upwardly directed surface of the main body 8 with which the lever 14 cooperates to grip the sheet, and this lever 14 is turnable downwardly in a clockwise direction, as viewed in FIG. 3, to the operating position illustrated in FIG. 3 where a sheet will be gripped between the lower curved surface of the lever 14 and the upwardly directed surface portion of the main body 8. The arrangement is such that as the force pulling the sheet in the direction of the arrow 5 of FIG. 3 increases the lever 14 and the cooperating upper wardly directed surface of the main body 8 grip the sheet tighter. Moreover, the end surface of the lever 14 which engages the sheet is convexly curved around an axis which also extends transversely across the drawing field, so that there are no sharp edges engaging the sheet and thus the sheet is in no way injured by the gripping lever 14. The gripping lever 15 turns transversely with respect to the drawing field and is turnable about an axis which extends substantially parallel to the drawing field in the direction of travel of the sheet during longitudinal stretching thereof. The gripping lever 15 serves to grip the sheet and absorb the forces encountered during transverse stretching of the sheet. As is apparent from FIGS. 4 and 5, the lever 15 also has a curved convex bottom end face engaging the sheet and cooperating with an upwardly directed surface of the main body 8 to grip the sheet. Moreover the lever 15 is turnable in a clockwise direction, as viewed in FIG. 5, downward to the illustrated operating position, so that the lower, gripping end of the lever 15 moves inwardly toward the center of the drawing field while the bottom end of the lever 15 advances toward the cooperating surface portion of the main body 8 to grip the sheet, and thus with this construction also as the transverse stretching forces increase the gripping force provided by the lever 15 also increases. At its rear end the main body 8 turnably carries a third gripping lever 16 which is substantially identical wtih the gripping lever 15 and which is supported for turning movement about an axis parallel to the axis of turning of the lever 15. It will be noted that the lever 15 is located forwardly of the lever 16 while the rear lever 16 is located inwardly of the forward lever 15. The purpose of the lever 16 is to hold the material or sheet which is transversely stretched by the lever 15 against any possible contraction at a portion of the sheet located to the rear of the lever 15. The several surface areas with which the bottom ends of the gripping levers 14-16 cooperate are all located in a common plane and form extensions of each other, so that the levers 1 4-16 all cooperate with a common surface portion of the main body 8 to grip the sheet 2 and support the latter during the longitudinal and transverse stretching thereof. Moreover, all of the gripping ends of the levers 14-16 are convexly curved and moreover the levers are free of any sharp edges which might dig into the sheet 2 and damage the latter.

It is possible to provide automatic control structures which cause levers such as the levers 15 and 16 to move to their operating positions engaging the sheet 2 only after the pair of gripping means 1 have been spaced from each other by a certain predetermined distance.

During operation of the structure shown in FIG. 1, a pair of the gripping means 1 will initially be located at starting positions at the entrance end of the drawing field adjacent to the entrance rollers 3 of the drawing means. At this location the several gripping levers 14-16 of the pair of gripping means 1 will be turned to their inoperative positions and the edge portions of the fabric will be placed on the upwardly directed surface portions of the main body 8 which cooperate with the bottom ends of the gripping levers 14-16. Then these gripping levers 14-16 are turned to their operating positions where they engage the upper surface of the sheet 2. If desired weights may be mounted on the levers 14-16 for automatically turning the latter to their operating positions, and FIG. 3 shows along the right edge of the lever 14 an extension which forms a weight which serves the purpose of urging the lever 14 to the illustrated operating position thereof. In the same way weights may be applied to the levers 15 and 16 or may be formed integrally therewith as shown for the lever 14 in FIG. 3.

With the opposed side edge portions of the sheet thus gripped by the pair of gripping means 1 the sets of drawing rollers 3 and 4 are set into operation and the pair of gripping means 1 will be guided by the guide means 7, 7' so as to advance with the sheet in the direction of the arrow 5 along the drawing field, and it will be noted that the sheet is supported by the pair of gripping means 1 during longitudinal as well as transverse stretching of the sheet 2. Because the guide means 7, 7 displaces the pair of gripping means 1 apart from each other as they advance along the drawing field with the sheet 2, the sheet 2 is necessarily stretched transversely as well as longitudinally. When the pair of gripping means 1 reach the discharge end of the drawing field, and they are shown adjacent to the discharge end of the drawing field in FIG. 1, the gripping levers 1416 are turned back to their inoperative positions, thus releasing the pair of gripping means so that they are free from the fabric or sheet 2 and can be returned to their starting positions, and beyond the discharge rollers 4 of the drawing means the sheet 2 which has been longitudinally and transversely stretched is delivered to further structure for the purpose of further handling and treating the sheet 2.

It will be understood that each of the elements de scribed above, or two or more together, wiil also find a useful application in other types of sheet stretching apparatus differing from the types described above.

While the invention has been illustrated and described as embodied in gripping devices for sheet stretching apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a sheet stretching apparatus for stretching a sheet longitudinally and transversely, in combination, drawing means for drawing a sheet longitudinally through a drawing field having entrance and discharge ends, said drawing means comprising two pairs of drawing rollers respectively located at said entrance and discharge ends, and means for rotating the pair of drawing rollers at said discharge end at a greater peripheral speed than the peripheral speed of the other pair of drawing rollers for longitudinally stretching said sheet as it is drawn through said drawing field; a plurality of independent gripping means for gripping the sheet at opposed side edge portions thereof, respectively, said gripping means being connected to each other only by the gripped sheet portions; and a pair of guide means respectively engaging said gripping means at opposite side edge portions for guiding said gripping means for movement through the drawing field with the sheet during the longitudinal stretching thereof by said drawing means, the distance between said pair of guide means increasing from said entrance end toward said discharge end so that the sheet is stretched transversely simultaneously with the longitudinal stretching thereof.

2. In a stretching apparatus for stretching a sheet both longitudinally and transversely, in combination, drawing means for drawing a sheet longitudinally through a drawing field having entrance and discharge ends said drawing means comprising two pairs of drawing rollers respectively located at said entrance and said discharge ends, and means for rotating the pair of drawing rollers at said discharge end at a greater peripheral speed than that of the other pairs of drawing rollers, for longitudinally stretching the sheet while the latter passes through the drawing field; a pair of elongated guide rods located at opposite sides of and extending along the drawing field, said rods being closer to each other adjacent the entrance end of the drawing field than at the discharge end of the drawing field; and a plurality of independent gripping means for respectively gripping a sheet at opposed side edge portions thereof while the sheet is drawn through the drawing field, said gripping means being connected to each other only by the gripped sheet portions, and said gripping means respectively including roller assemblies which engage and ride on said rods, respectively, so that said rods guide said gripping means for movement with the sheet through the drawing field while increasing the distance between the gripping means at opposite side edge portions as the gripping means advance with the sheet in the drawing field so that the sheet is stretched transversely simultaneously with the longitudinal stretching thereof.

3. In a sheet stretching apparatus for stretching a sheet both longitudinally and transversely, in combination, drawing means for drawing a sheet longitudinally through a predetermined drawing field having entrance and discharge ends said drawing means comprising two pairs of drawing rollers respectively located at said entrance and said discharge ends, and mean for rotating the pair of drawing rollers at said discharge end at a greater peripheral speed than that of the other pair of drawing rollers, so that the sheet is longitudinally stretched while advancing longitudinally through the drawing field; a pair of guide rods of substantially circular cross section respectively located at opposite sides of and extending along the drawing field; and a plurality of independent gripping means for respectively gripping a sheet at opposed side edge portions thereof, said gripping means being connected to each other only by the gripped sheet portions, said gripping means respectively including roller assemblies which engage said guide rods to be guided thereby for movement with the sheet longitudinally through the drawing field, said guide rods being spaced apart from each other adjacent the discharge end of the drawing field by a distance greater than the distance between said rods at portions thereof adjacent the entrance end of the drawing field, so that the gripping means at opposite side edge portions become more distant from each other as they advance through the drawing field to stretch the sheet transversely simultaneously with the longitudinal stretching thereof, and each of said roller assemblies including a pair of rollers each of which have outer concave peripheries engaging the guide rod.

4. In a sheet stretching apparatus, in combination, drawing means for drawing a sheet longitudinally through a drawing field while simultaneously stretching the sheet longitudinally; guide means extending along opposite sides of the drawing field; and a pair of gripping means for gripping a sheet at opposed side edge portions thereof and guided by said guide means for movement with the sheet longitudinally along the drawing field, said guide means increasing the distance between said pair of gripping means as the latter advance with the sheet through the drawing field so that the sheet is stretched transversely simultaneously with the longitudinal stretching thereof, each gripping means including a main body and a pair of gripping levers turnably carried by said main body for turning movement to and from gripping posiitons, said levers being respectively turnable about a pair of axes which are substantially perpendicular to each other and one of which extends substantially in the longitudinal direction of advance of the sheet along the drawing field while the other extends transversely to said longitudinal direction.

5. In a sheet stretching apparatus, in combination, drawing means for drawing a sheet longitudinally through a drawing field while simultaneously stretching the sheet longitudinally; guide means extending along opposite sides of the drawing field; and a pair of gripping means for gripping a sheet at opposed side edge portions thereof and guided by said guide means for movement with the sheet longitudinally along the drawing field, said guide means increasing the distance between said pair of gripping means as the latter advance with the sheet through the drawing field so that the sheet is stretched transversely simultaneously with the longitudinal stretching thereof, each gripping means including a main body and a pair of gripping levers turnably carried by said main body for turning movement to and from gripping positions, said levers being respectively turnable about a pair of axes which are substantially perpendicular to each other and one of which extends substantially in the longitudinal direction of advance of the sheet along the drawing field while the other extends transversely to said longitudinal direction, said levers of each gripping means respectively having gripping ends which cooperate with a common surface portion of said main body for gripping a sheet between said ends of said levers and said common surface portion of said main body.

6. In a sheet stretching apparatus, in combination, drawing means for drawing a sheet longitudinally through a drawing field while simultaneously stretching the sheet longitudinally; guide means extending along opposite sides of the drawing field; and a pair of gripping means for gripping a sheet at opposed side edge portions thereof and guided by said guide means for movement with the sheet longitudinally along the drawing eld, said guide means increasing the distance between said pair of gripping means as the latter advance with the sheet through the drawing field so that the sheet is stretched transversely simultaneously with the longitudinal stretching thereof, each gripping means including a main body and a pair of gripping levers turnably carried by said main body for turning movement to and from gripping positions, said levers being respectively turnable about a pair of axes which are substantially perpendicular to each other and one of which extends substantially in the longitudinal direction of advance of the sheet along the drawing field while the other extends transversely to said longitudinal direction, said levers of each gripping means respectively having gripping ends which cooperate with a common surface portion of said main body for gripping a sheet between said ends of said levers and said common surface portions of said main body, said drawing field being substantially horizontal and the turning axes of the pair of levers of each gripping means being located above the drawing field over the common surface portion of the main body with which the ends of said levers cooperate and said turning axes of said levers being located in a plane substantially parallel to the drawing field.

7. In a sheet stretching apparatus for stretching a sheet both longitudinally and transversely, in combination, drawing means for drawing the sheet longitudinally through a drawing field while longitudinally stretching the sheet; guide means extending along opposite sides of the drawing field; and a pair of gripping means for gripping the sheet at opposed side edge portions thereof, respectively, said pair of gripping means being guided by said guide means for movement with the sheet as the latter advances longitudinally along the drawing field and said guide means increasing the distance between said pair of gripping means as the latter advance with the sheet along the drawing field so that the sheet is stretched transversely simultaneously with the longitudinal stretching thereof, each gripping means including a main body and a gripping lever turnably carried by said main body for turning movement about an axis which extends substantially transversely across the drawing field, said gripping lever being turnable from an inoperative position substantially in the direction of advance of the sheet along the drawing field to an operative position where an end of said lever is located closely adjacent to a surface portion of said main body for gripping the sheet between said end of said lever and said surface portion of said main body.

8. In a sheet stretching apparatus for stretching a sheet both longitudinally and transversely, in combination, drawing means for drawing the sheet longitudinally through a drawing field while longitudinally stretching the sheet; guide means extending along opposite sides of the drawing field; and a pair of gripping means for gripping the sheet at opposed side edge portions thereof, respectively, said pair of gripping means being guided by said guide means for movement with the sheet as the latter advances longitudinally along the drawing field and said guide means increasing the distance between said pair of gripping means as the latter advance with the sheet along the drawing field so that the sheet is stretched transversely simultaneously with the longitudinal stretching thereof, each gripping means including a main body and a gripping lever turnably carried by said main body for turning movement about an axis which extends substantially transversely across the drawing field, said gripping lever being turnable from an inoperative position substantially in the direction of advance of the sheet along the drawing field to an operative position Where an end of said lever is located closely adjacent to a surface portion of said main body for gripping the sheet between said end of said lever and said surface portion of said main body, and each gripping means including a second gripping lever turnable about an axis which extends in the same general direction as the direction which the sheet advances along the drawing field, said second gripping lever being displaced rearwardly with respect to said firstmentioned gripping lever in the direction of advance of the sheet along the drawing field and said second lever having a free end which cooperates with an extension of the surface portion of said main body with which said first-mentioned lever cooperates for gripping the sheet.

9. In a sheet stretching apparatus for stretching a sheet both longitudinally and transversely, in combination, drawing means for drawing the sheet longitudinally through a drawing field While longitudinally stretching the sheet; guide means extending along opposite sides of the drawing field; and a pair of gripping means for gripping the sheet at opposed side edge portions thereof, respectively, said pair of gripping means being guided by said guide means for movement with the sheet as the latter advances longitudinally along the drawing field and said guide means increasing the distance between said pair of gripping means as the latter advance with the sheet along the drawing field so that the sheet is stretched transversely simultaneously with the longitudinal stretching thereof, each gripping means including a main body and a gripping lever turnably carried by said main body for turning movement about an axis which extends substantially transversely across the drawing field, said gripping lever being turnable from an inoperative position substantially in the direction of advance of the sheet along the drawing field to an operative position where an end of said lever is located closely adjacent to a surface portion of said main body for gripping the sheet between said end of said lever and said surface portion of said main body, and each gripping means including a second gripping lever turnable about an axis which extends in the same general direction as the direction which the sheet advances along the drawing field, said second gripping lever being displaced rearwardly with respect to said first-mentioned gripping lever in the direction of advance of the sheet along the drawing field and said second lever having a free end which cooperates with an extension of the surface portion of said main body with which said first-mentioned lever cooperates for gripping the sheet, and said second levers of said pair of gripping means being located closer to each other than said first-mentioned levers.

10. In a stretching apparatus for stretching a sheet both longitudinally and transversely, in combination, drawing means for drawing a sheet longitudinally through a substantially horizontal drawing field while stretching the sheet longitudinally along the drawing field; support means having at least a pair of supporting surface portions respectively located adjacent ends of the drawing field beneath the latter; guide means extending along the drawing field at opposite sides thereof; and a pair of gripping means for respectively gripping a sheet at opposed side edge portions thereof, said pair of gripping means being guided by said guide means for movement with a sheet longitudinally along the drawing field and said guide means increasing the distance between said pair of gripping means as the latter advance together with a sheet along the drawing field so that the sheet is stretched transversely simultaneously with the longitudinal stretching thereof, each gripping means having a lower portion carrying at least one roller which turns about a substantially horizontal axis parallel to the drawing field and extending transversely with respect thereof, and said roller being adapted to engage said surface portions of said support means for positioning said gripping means substantially horizontally at least adjacent the ends of the drawing field.

11. In a sheet stretching apparatus for stretching a sheet both longitudinally and transversely, in combination, drawing means for drawing a sheet longitudinally through a drawing field while stretching the sheet longitudinally; a pair of elongated guide rods respectively located at opposite sides of and extending along the drawing field, said drawing field having entrance and discharge ends and said guide rods being spaced from each other at'said discharge end of said drawing field by a distance greater than the distance between said rods at said entrance end of said field; and a plurality of independent gripping means for gripping a sheet respectively at opposed side edge portions thereof, said gripping means respectively including roller assemblies which engage said rods so that the latter guides said gripping means for movement with a sheet longitudinally along the drawing field, and said rods increasing the distance between said gripping means as the latter advance with the sheet along the drawing field to stretch the sheet transversely simultaneously with the longitudinal stretching thereof, each gripping means having a leading end which is located at a front portion of each gripping means in the direction of advance of the sheet along the drawing field and said roller assemblies of each gripping means including a roller located at the leading end of each gripping means and engaging the guide rod so that said roller may be used for locating the gripping means at a selected position along the guide rod and for maintaining a minimum distance between adjacent gripping means. i

12. A sheet gripping device for use in a sheet stretching apparatus, said device including a main body having an inner end located adjacent to and an outer end located distant from a drawing field in which a sheet which is gripped by the gripping device is stretched, said main body also having front and rear ends and said front end of said main body preceding said rear end thereof in the direction of travel of the gripping device with a sheet along the drawing field, said main body pivotally supporting a pair of gripping levers for turning movement about axes which are parallel to each other and which extend in the general direction of advance of the gripping device with the sheet along the drawing field and said levers being displaced both longitudinally and transversely on said main body with the front end of said pair of levers being 11 12 located nearer to the outer end of said main body than 2,923,966 2/60 Tooke et a1. 18-1 the rear one of said l ver 3,046,599 7/62 Nicholas et a1. 18-1 References Cited by the Examiner FOREIGN PATENTS UNITED STATES PATENTS 5 1,111,812 7/61 Germany.

2,473,404 6/49 Young 18 1 WILLIAM J. STEPHENSON, Primary Examiner.

2,530,119 11/50 Dungler 2661 

1. IN A SHEET STRETCHING APPARATUS FOR STRETCHING A SHEET LONGITUDINALLY AND TRANSVERSELY, IN COMBINATION, DRAWING MEANS FOR DRAWING A SHEET LONGITUDINALLY THROUGH A DRAWING FIELD HAVING ENTRANCE AND DISCHARGE ENDS, SAID DRAWING MEANS COMPRISING TWO PAIRS OF DRAWING ROLLERS RESPECTIVELY LOCATED AT SAID ENTRANCE AND DISCHARGE ENDS, AND MEANS FOR ROTATING THE PAIR OF DRAWING ROLLERS AT SAID DISCHARGE END AT A GREATER PERIPHERAL SPEED THEN THE PERIPHERAL SPEED OF THE OTHER PAIR OF DRAWING ROLLERS FOR LONGITUDINALLY STRETCHING SAID SHEET AS IT IS DRAWN THROUGH SAID DRAWING FIELD; A PLURALITY OF INDEPENDENT GRIPPING MEANS FOR GRIPPING THE SHEET AT OPPOSED SIDE EDGE PORTIONS THEREOF, RESPECTIVELY, SAID GRIPPING MEANS BEING CONNECTED TO EACH OTHER ONLY BY THE GRIPPING SHEET PORTIONS; AND A PAIR OF GUIDE MEANS RESPECTIVELY ENGAGING SAID GRIPPING MEANS AT OPPOSITE SIDE EDGE PORTIONS FOR GUIDING SAID GRIPPING MEANS FOR MOVEMENT THROUGH THE DRAWING FIELD WITH THE SHEET DURING THE LONGITUDINAL STRETCHING THEREOF BY SAID DRAWING MEANS, THE DISTANCE BETWEEN SAID PAIR OF GUIDE MEANS INCREASING FROM SAID ENTRANCE END TOWARD SAID DISCAHRGE END SO THAT THE SHEET IS STRETCHED TRANSVERSELY SIMULTANEOUSLY WITH THE LONGITUDINAL STRETCHING THEREOF. 